This invention relates to an improved process for preparation of conjugated linoleic acid (CLA) from oils rich in linoleic acid, which overcomes problems with an intractable emulsion that occurs between CLA and water by treatment with either an alcohol or polyethylene glycol or a tannin. The reaction is also unique in that it allows the control of the production of positional isomers in the conjugated linoleic acid. The process by-product stream is usable directly as a fertilizer that limits waste disposal costs.
Conjugated linoleic acid is the trivial name given to a series of eighteen carbon diene fatty acids with conjugated double bonds. Applications of conjugated linoleic acids vary from treatment of medical conditions such as anorexia (U.S. Pat. No. 5,430,066) and low immunity (U.S. Pat. No. 5,674,901) to applications in the field of dietetics where CLA has been reported to reduce body fat (U.S. Pat. No. 5,554,646) and to inclusion in cosmetic formulae (U.S. Pat. No. 4,393,043).
CLA shows similar activity in veterinary applications. In addition, CLA has proven effective in reducing valgus and varus deformity in poultry (U.S. Pat. No. 5,760,083), and attenuating allergic responses (U.S. Pat. No. 5,585,400). CLA has also been reported to increase feed conversion efficiency in animals (U.S. Pat. No. 5,428,072). CLA-containing bait can reduce the fertility of scavenger bird species such as crows and magpies (U.S. Pat. No. 5,504,114).
Industrial applications for CLA also exist where it is used as a lubricant constituent (U.S. Pat. No. 4,376,711). CLA synthesis can be used as a means to chemically modify linoleic acid so that it is readily reactive to Diels-Alder reagents (U.S. Pat. No. 5,053,534). In one method linoleic acid was separated from oleic acid by first conjugation then reaction with maleic anhydride followed by distillation (U.S. Pat. No. 5,194,640).
Conjugated linoleic acid occurs naturally in ruminant depot fats. The predominant form of CLA in ruminant fat is the cis,trans-9,11-octadecadienoic acid which is synthesized from linoleic acid in the rumen by micro-organisms like Butryvibrio fibrisolvens. The level of CLA found in ruminant fat is in part a function of dietary cis, cis-9,12-octadecadienoic acid and the level of CLA in ruminant milk and depot fat may be increased marginally by feeding linoleic acid (U.S. Pat. No. 5,770,247).
CLA may also be prepared by any of several analytical and preparative methods. Pariza and Ha xe2x80x9cpasteurizedxe2x80x9d a mixture of butter oil and whey protein at 85xc2x0 C. for 5 minutes and noted elevated levels of CLA in the oil (U.S. Pat. No. 5,070,104). CLA produced by this mechanism is predominantly a mixture of cis,trans-9,11-octadecadienoic acid and trans,cis-10,12-octadecadienoic acid.
CLA has also been produced by the reaction of soaps with strong alkali bases in molten soaps, alcohol, and ethylene glycol monomethyl ether (U.S. Pat. Nos. 2,389,260; 2,242,230 and 2,343,644). These reactions are inefficient as they require the multiple steps of formation of the fatty acid followed by production of soap from the fatty acids, and subsequently increasing the temperature to isomerize the linoleic soap. The CLA product is generated by acidification with a strong acid (sulfuric or hydrochloric acid) and repeatedly washing the product with brine or CaCl2.
CLA has been synthesized from fatty acids using SO2 in the presence of a sub-stoichiometric amount of soap forming base (U.S. Pat. No. 4,381,264). The reaction with this catalyst produced predominantly the all trans configuration of CLA.
Efficient synthesis of cis,trans-9,11-octadecadienoic from ricinoleic acid has been achieved (Russian Patent 2,021,252). This synthesis, although efficient, uses expensive elimination reagents such as 1,8-diazobicyclo-(5,4,0)-undecene. For most applications the cost of the elimination reagent increases the production cost beyond the level at which commercial production of CLA is economically viable.
Of these methods alkali isomerization of soaps is the least expensive process for bulk preparation of CLA isomers, however, the use of either monohydric or polyhydric alcohols in alkali isomerization of CLA can be problematic. Lower alcohols are readily removed from the CLA product but they require the production facility be built to support the use of flammable solvents. Higher molecular weight alcohols and polyhydric alcohols are considerably more difficult to remove from the product and residual levels of these alcohols (e.g. ethylene glycol) may not be acceptable in the CLA product.
Water may be used in place of alcohols in the production of CLA by alkali isomerization of soaps (U.S. Pat. Nos. 2,350,583 and 4,164,505). When water is used for this reaction it is necessary to perform the reaction in a pressure vessel whether in a batch (U.S. Pat. No. 2,350,583) or continuous mode of operation (U.S. Pat. No. 4,164,505). The process for synthesis of CLA from soaps dissolved in water still requires a complex series of reaction steps. Bradley and Richardson (Industrial and Engineering Chemistry February 1942 vol 34 no2 237-242) were able to produce CLA directly from soybean triglycerides by mixing sodium hydroxide, water and oil in a pressure vessel. Their method eliminated the need to synthesize fatty acids and then form soaps prior to the isomerization reaction. However, they reported that they were able to produce an oil with up to 40 percent CLA. Quantitative conversion of the linoleic acid in soybean oil to CLA would have produced a fatty acid mixture with approximately 54 percent CLA.
Commercial conjugated linoleic acid often contains a mixture of positional isomers that may include trans,cis-8,10-octadecadienoic acid, cis,trans-9,11-octadecadienoic acid, trans,cis-10,12-octadecadienoic acid, and cis,trans-11,13-octadecadienoic acid (Christie, W. W., G. Dobson, and F. D. Gunstone, (1997) xe2x80x9cIsomers in commercial samples of conjugated linoleic acid.xe2x80x9d J. Am. Oil Chem. Soc. 74,11,1231). Sebedio et al. (Inform Volume 10. No.5) prepared highly enriched CLA acids isomers and studied their effects on rat tissue lipids. They reported that virtually all of the biological activity of the mixed CLA isomers could be attributed to trans,cis-10,12-octadecadienoic acid while very little activity could be ascribed to the cis,trans-9,11-octadecadienoic acid isomer. A commercial reaction to prepare CLA should therefore produce an enriched fraction of trans,cis-10,12-octadecadienoic acid.
The present invention describes a method of production of CLA using water as a reaction medium and a vegetable oil containing more than 60% linoleic acid. The reaction in water produces several isomers but the isomer ratio is controlled by the addition of modifiers and reaction kinetics. The reaction products may be specifically enriched in trans, cis-10,12-octadecadienoic acid the most active CLA isomer in many assays of CLA activity. The catalytic reaction in alkali is uniquely useful in producing deuterium and tritium labelled isomers of CLA that is achieved by conducting the reaction in deuterated or tritiated water. Isotopically labelled CLA is useful in metabolic studies of CLA metabolism.
When this product is quantitatively converted to CLA it forms an intractable emulsion that is not readily broken using conventional techniques of resolving emulsions such as freezing, heating and centrifugation. Other researchers have used conventional methods to wash and dehydrate the CLA isomers with solutions of CaCl2 when the CLA content of the fatty acids is below 50%. We have found that these methods are not suitable for breaking emulsions caused by solutions that contain over 60% CLA.
In the present invention the quantitative production of CLA from linoleic acid rich oils is achieved by hydrolysis and isomerization with base in a single step reaction in water, deuterated water or tritiated water and the physical separation of the fatty acids from the water or isotopically labelled water after isomerization. A preferred embodiment entails the addition of 45% aqueous potassium hydroxide as the base/catalyst; thereafter, the reaction mixture is neutralized by a strong acid, with 70% H3PO4 being preferred. The selection of H3PO4 as the acid and KOH as the base allow the aqueous salt solution to be disposed of in surface applications such as a liquid or solid fertilizer. The neutralized reaction mixture forms an emulsion that can be separated only by the addition of demulsifiers. The demulsifier used to break the emulsion formed by CLA and water must be inexpensive and suitable for the production of food, cosmetic and medicinal products. It has now been found that the emulsions between CLA and water can be broken using polyethylene glycol, ethanol or other monohydric alcohol or tannin (hydrolysable or condensed) or fulvic acid or humic acid. The reaction can also be controlled to minimize the production of undesirable isomers. The major element of control is through the vigorous agitation of the CLA reaction mixture during synthesis. Refining of CLA with solid phase refining methods is also contemplated. The partial enrichment and concentration of specific CLA isomers using crystallization from organic solvent is also contemplated.
This invention provides a process for producing a conjugated linoleic acid-rich fatty acid mixture comprising reacting a linoleic acid-rich oil with a base in the presence of a catalytic amount of said base in an aqueous medium at a temperature above 170xc2x0 C., and separating said conjugated linoleic acid-rich fatty acid mixture from said aqueous medium.